Black Powder Rockets

[Karl]

Now I getting realy pisst off, I can´t make the rocket fly and I can´t understand WHY!?!?

 

Help me!!!

 

I`m making endburners the measurement is this

 

Length is 90 mm

The diamter of the tube is 13 mm and the walls are 4 mm thick and very hard

The plugs is made in cat clay and very hard.

 

I have tryd very many combinations and this is some of them.

 

The weight of a complete rocket is 60 g and the fuel (Bp) weight 10g.

 

Slow BP

Nozzel 3mm 2,5mm core flyd slowly tp 0,7 m upp and then then the thrust was to low to continve and i fell back

Nozzel 2,5 mm, core 2,5 mm CATO

 

Fast BP

Nozzel 5mm, core 4mm, fly 5m and then lost all thrust

Nozzel 4,5mm, core 4, a really big bang.

 

What in hell is wrong???

 

/ Bug

Couple questions first, are they cored, or end burners? You start off saying they are end burners, but then go one in the examples and they all have cores. Either way, it sounds like your nozzle size is too small. I had the problem to start with. A nozzle too small will not give the rocket enough thrust, causing a slow take off and in some cases it gets pissed and just CATO's. If you haven't already, try a larger nozzle and see if that works.

The core is very short to have a place to put the fuse, is this wrong?

 

Smaller nozzel means more thurs, or is I´m wrong?

 

I mean that smaller nozzel will make more pressuer inside the motor and more pressuer make the BP to burn faster = more thrus

 

Big nozzel = less perssuer = less thrust.

 

And like you see in my post I have test the nozzel where the motor is on the limet to brake / cato.

 

/ Bug

Yes you are right, Bug_X.

 

Small nozzle + Long Core = Higher initial thrust but shorter burn time

Larger nozzle + Short Core = Less thrust and longer burn time

[ActionTekJackson]

Now I getting realy pisst off, I can´t make the rocket fly and I can´t understand WHY!?!?

 

Help me!!!

 

I`m making endburners the measurement is this

 

Length is 90 mm

The diamter of the tube is 13 mm and the walls are 4 mm thick and very hard

The plugs is made in cat clay and very hard.

 

I have tryd very many combinations and this is some of them.

 

The weight of a complete rocket is 60 g and the fuel (Bp) weight 10g.

 

Slow BP

Nozzel 3mm 2,5mm core flyd slowly tp 0,7 m upp and then then the thrust was to low to continve and i fell back

Nozzel 2,5 mm, core 2,5 mm CATO

 

Fast BP

Nozzel 5mm, core 4mm, fly 5m and then lost all thrust

Nozzel 4,5mm, core 4, a really big bang.

 

What in hell is wrong???

 

/ Bug

Couple questions first, are they cored, or end burners? You start off saying they are end burners, but then go one in the examples and they all have cores. Either way, it sounds like your nozzle size is too small. I had the problem to start with. A nozzle too small will not give the rocket enough thrust, causing a slow take off and in some cases it gets pissed and just CATO's. If you haven't already, try a larger nozzle and see if that works.

The core is very short to have a place to put the fuse, is this wrong?

 

Smaller nozzel means more thurs, or is I´m wrong?

 

I mean that smaller nozzel will make more pressuer inside the motor and more pressuer make the BP to burn faster = more thrus

 

Big nozzel = less perssuer = less thrust.

 

And like you see in my post I have test the nozzel where the motor is on the limet to brake / cato.

 

/ Bug

Yes you are right, Bug_X.

 

Small nozzle + Long Core = Higher initial thrust but shorter burn time

Larger nozzle + Short Core = Less thrust and longer burn time

This is true, but only to a point. There may be more pressure, but that pressure has to exit the nozzle fast enough to make the rocket fly. I can't really explain the technicalities, I only know its true. I've done many tests, and I couldn't figure out why my rockets were taking off so slow, and arcing. I tried making faster propellents but that didn't help. Once I increased the nozzle size it flew great.

[rocket]

If you make the nozzle to small it may CATO for a build up of too much presser.

Correct me if I’m wrong.

[ActionTekJackson]

More often than not that is correct. However, if your propellant is a slow one it may not cato, but just sit there, or have very slow/lazy take off.

[Silverturk]

If I make a nozzle that is bigger than 4 mm, it will only become something like a fountain, and at least 10 SEK burn time, which I guess suck. Even harder than my really bad BP.

 

 

Action-jackson , what different rocket dimensions are you using? How long core, what ype of BP etc.

[ActionTekJackson]

I use 3/4" ID in 3 1/2" and 6" lengths, with a 3/8" nozzle with a full core the same diameter. I will get back to you on the BP burn time, I have a guess but I wanna be absolutely sure so I'll run a few tests and average it out.

[d4j0n]

I've been looking around to find where I can buy steve majdali's bottle rocket tooling...

[optimus]

I use 3/4" ID in 3 1/2" and 6" lengths, with a 3/8" nozzle with a full core the same diameter.

When you say a full core, do you mean the core extends all the way through the grain?

[ActionTekJackson]

I use 3/4" ID in 3 1/2" and 6" lengths, with a 3/8" nozzle with a full core the same diameter.

When you say a full core, do you mean the core extends all the way through the grain?

That would be correct.

[Silverturk]

How long burn time do your rockts have?

[ActionTekJackson]

The burn time for my 3 1/2" is about 4-5 sec. and for the 6" 9-10 sec. However, for the 3 1/2" its roughly 7 sec. before it reaches apogee, and 13 sec. for the 6". The 3 1/2" rockets reach about 200-250 ft, and the 6" 400-500 ft easy. Can't say for sure, have to judge it with me eyes.

 

 

~Just a note, I also prime my cores with a loose filling of BP, to help ensure the entire core ignites at once, or at least more of it does. This isn't absolutely neccessary, but it does make them take off faster.

[d4j0n]

About sticks attatched to rockets, what's the advantage of having a light long one as opposed to a shorter heavier one? Is there an optimal weight and legnth?

 

Where do you guys get your sticks from? All I've ever done was stick bamboo skewers together to make longer sticks. I've heard that you shouldn't use wire but I don't see why...a stick would still poke your eye out.

[Pyrohawk]

I just rip pieces of pin off of boards I have laying around. Since I don't store them for any period of time warping isn't really a problem. If they're small I just go with a dowel rod!

[justanotherpyro]

Well, a 2" long rock that weighs 50g will not work as well as a 30" long piece of bamboo that weighs 50g, obviously. Even though they both balance the stick works better. Which leads me to believe that weight can be the constant factor, and length can vary. If your engine works well with a 25 g stick then you can make it as long as you want (within reason).

 

Correct me if I'm wrong, because this is all speculation. It has worked in my tests though.

[Silverturk]

The important thing is that the rocket is balanced just below the rocket nozzle. If you use a short stick it will have to be very heavy. Imagine that your stick is only 10 cm. This would mean that the stick would have to wheigt as much as the rocket, or even more. But if you use a long stick, it can be lighter in wheigt and the rocket is still balanced.

[al93535]

The rocket does not have to be balanced. None of my rockets are even close to being balanced. I use certian length sticks for certian sized motors. For my 1 lb motors, I use a 36" stick no matter what.

 

When the rocket is flying through the air at a high speed the air rushing by the stick pushes it straight back, rather like a weather vane. This seems to work alot better with a high initial thrusting rocket. As you can see from my end burning videos the rocket seems to veer to the side. My core burners go alot straighter.

[Silverturk]

Really? I didnt know that has only heard that the rocket had to be balanced if you put your finger in the nozzle...

[hst45]

al, that makes sense. I bet that the flat stick tends to stabilize the rocket better at slower speed, sort of like a rudder. If the flight starts to go off line the flat stick might offer greater wind resistance and therefor drag the tail back in line. I suspect that once the rocket reaches a sufficient velocity both types of sticks are comparable, but perhaps the flat stick stabilizes the rockets flight more quickly. which would tend to explain why your end-burners are less stable.

 

Sorry, this is just a theory. I will make a couple of test motors and test this the next time a make rockets.

[al93535]

I have heard arguments both ways, square is best, round is best, and it makes no difference. I always used round on my end burners. Now I always use square sticks on the core burners. So I am unable to say which works best.

 

I do have a 1lb core burner with a round stick here, I will post its video when I light it. As well as with a few others 1 lbers with square sticks.

 

But I must say, there is more mass on a square stick then of an equal diameter round stick. Because you can imagine a round stick inside the square one, the square just has edges. Maybe that has something to do with it.

[brainfever]

IIRC it all has to do with surface area.

 

A square stick of the same mass and length will have a greater surface area then a round stick, so in theory it should balance your rocket better. Even if made out of a lighter material to make up for the otherwise extra mass.

 

Rocket physics don't seem all that hard, I just have some more reading to do ... if I only had the time

 

Meanwhile, if you want your round stick to have some more surface, try splitting it and slip a "rudder" in it made out of hard plastic or something. Think of the feather on an arrow and you'll know what I mean.

[justanotherpyro]

If you lit a powerfull short burning engine without a stick, it very well could go straight after it hit a certain velocity. The balancing of the stick I can definately agree is for a motor that doesn't give out a lot of thrust.

 

For example, a half cored KNO3 rocket that Actiontekjackson made, and I witnessed, had a very long burn time, and a low thrust. It definately made it off of the ground and went high but it arced really bad. The frames of video right as it launched show it tilt within the first few feet because it was unbalanced. If it would have had a substantially higher ammount of thrust, like Al said, it wouldn't have mattered.

 

Those slower rockets are a nice effect with their long burn time, but need to be balanced to prevent the arcing problem.

 

The way I figure all of this is if you threw a baseball really weak it arcs within a few feet. If it was shot at 200 mph it would travel straight for a long distance and time before arcing.

[psymon]

I often make rockets. I try to make them balance below the nozzle, however more often than not they do not balance. Most of the time I try to make them not balance because I can then use less weight and theoretically my rockets go higher. Lets face it, the rocket will change weight throughout its burn. It will get lighter and lighter the more powder it burns. So it will always be unbalanced shortly after ignition.

I would say that you should get the rocket balanced and then chop off a few inches of stick to unbalance it to gain greatest height.

[justanotherpyro]

There are several ways to view that. The balancing of the low thrust rocket that I mentioned is important because it won't go straight on its own because of its thrust. So yes as it gets lighter it could start to arc at a certain height or weight. The only thing though, is that arcing is caused by being top heavy, it would be bottom heavy, and thus I don't think it would arc.

 

I feel that proper balance is only really necessary to give it a good straight take off if its a medium speed burning rocket. If its a slow burning low thrust rocket, balancing is very important for the whole flight, and that its ok for it to be bottom heavy as long as it starts off balanced. Lastly that balancing isn't important for the fast burning rockets, the payload lifters, becasue they can overcome the gravitational pull before initial arcing occurs.

 

These are all in the no atmospheric resistance world though. Wind can tilt a rocket 10 degrees, which will then send it arcing across the sky.

[ActionTekJackson]

Proof of the slow comp. needing to be balanced theory. Here is a video of a Mg/BP/KNO3/Sucrose Hybrid Rocket I have that wasn't balanced. I put a salute payload on it as well. As you can see it arcs pretty bad, hence me exclaiming "Crap..."

 

3/4" x 3 1/2" Mg/BP/Sucrose Hybrid Rocket with Payload

[hst45]

Justanotherpyro, that makes sense. I seem to remember some technical data that I saw years ago about the Congreave (spelling?) rockets that the British uses in the 1700's. Weren't they launched from "V" shaped half-tubes? Perhaps it would be useful to start a low initial thrust rocket inside a tube to get it started in the right direction. By the time it developed enough velocity to leave the tube it might be relatively more stable than from a stick-in-the-ground start.

 

If you want a vertical flight i would think that a rather heavy "tail", or one with a larger coefficient of drag, would be best as this would always try to find plumb flight. For lateral, balistic flight, i want to try brainfever's fins-on-the-tail idea to keep the rockets trajectory in the same vector in which it started. This could yield good stability with lower mass, resulting in longer flight and/or greater payload capacity.

 

Excuse me a minuite, the wife's here. "Sure honey, I'd love to go with you to see mother, but I have to make a few more rockets. A scientists work is never done!!! No honey, don't go away mad." (door slams) Damn, i thought she'd never leave!! TO THE WORKSHOP!!!!!

 

By the way Brainfever, damn good site! Your synthesises are elegantly simple! I particularly like the KNO3 "because i can."